1. Field of the Disclosure
This disclosure relates generally to the field of drilling systems, biasing mechanisms for use with drilling systems, and methods for directionally orienting downhole assemblies, including directionally drilling boreholes.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Wells, or boreholes, are generally drilled in the ground to recover natural deposits of hydrocarbons and other desirable materials trapped in geological formations in the Earth's crust. A drill bit is attached to the lower end of a drill string suspended from a drilling rig. The drill string is a long string of sections of drill pipe that are connected together end-to-end to form a long shaft for moving the drill bit into the Earth. Drilling fluid, or “mud”, is typically pumped down through the drill string to the drill bit. The drilling fluid may not only lubricate and cool the drill bit, but it may also be used to drive a mud motor.
Directional drilling is the intentional deviation of the borehole from the path it would naturally take when the borehole is drilled by advancing a drill bit into the Earth, whereby a portion of the borehole is inclined at an angle with respect to the vertical and with the inclination having a particular compass heading or azimuth. In directional assemblies, the drill bit has a “toolface” angle. The toolface angle is the relative position of the angle of the bit shaft, to which the drill bit is attached, to the high side of the borehole. This toolface angle is the offset from the high side of the borehole in which the drill bit is deviated when viewed from a plane perpendicular to the longitudinal axis of the borehole. The high side of the borehole can be determined based on the Earth's gravitational field. The Earth's magnetic field can also be used for the determination of borehole high-side. The high-side is determined with the magnetic field vector and specific understanding of the borehole's location in latitude and longitude on the Earth. As a borehole is drilled, the toolface angle determines the direction the borehole is drilled and subsequently the borehole's inclination, or the angle with respect to gravity and the borehole's azimuth, or compass heading, when viewed from above the Earth's surface.
Currently, directionally drilling of oil and gas wells is typically done with either a mud motor or with a Rotary Steerable System (“RSS”). With mud motor based directional drilling methods, the rotation of the drill string is stopped and the mud motor's orientation is accomplished by orienting the drill pipe, or drill string, from the Earth's surface to point the mud motor in a new direction typically by lifting the mud motor upwardly from the bottom of the borehole, or off-bottom, and then rotating the drill string to point the mud motor in the desired new direction. The mud motor based directional drilling system is then pushed forward without rotation of the drill pipe, which is generally referred to as a “slide”. During a slide, only the drill bit is rotating as it is driven by the mud motor. The toolface angle, or toolface, which establishes the new trajectory for the borehole to be drilled determines both the inclination, or angle with respect to gravity and the azimuth, or compass heading, at which the directional drilled borehole will be drilled. For drilling a straight borehole, the drill string is rotated from surface, subsequently rotating the mud motor and bent housing to drill forward. During such rotational drilling, the resulting borehole diameter is slightly larger than the gauge diameter of the drill bit due to the rotation of the bent housing typically used in such drilling.
An RSS uses complex, electromechanical systems that include sensors, onboard computers, and advanced control systems to continuously orient the drill bit in the desired direction, while the entire RSS and drill pipe continue to rotate.